The overall aim of this quantitative, positron emission tomography (PET)-based, stroke outcome study on symptomatic patients with carotid occlusive vascular disease (OVD), is to determine whether patients identified in hemodynamic compromise by cerebrovascular reserve (CVR) (threshold, 10%) but with normal OEF (threshold, 50%) remain at increased risk for new clinical and magnetic resonance imaging (MRI)- based stroke. Symptomatic patients diagnosed with carotid OVD (n=150) are categorized into different stages of hemodynamic compromise by PET measurements of quantitative cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate for oxygen (CMRO2) before and after 15 mg/kg acetazolamide to obtain CVR and the oxygen extraction fraction response (OEFR). Qualitative measurements of CVR and OEF are also made by the count-rate ratio method to evaluate the accuracy of qualitative versus quanitative measures in predicting stroke risk. Baseline neurologic examination, neurologic scoring, and MRI are recorded for prestudy neurologic status and cortical and subcortical white matter infarctions. MRI and PET studies in a cohort of normal, healthy, volunteers (n=30) will be used to define the CVR and OEF thresholds to identify the different stages of hemodynamic compromise. The stages of hemodynamic compromise are as follows: Stages I and II, CVR>10%, OEF <50%;Stage Ill-acute, CVR<10% and OEF>50%;and Stage Ill-chronic, CVR<10%, OEF<50%. The different stages are also characterized by PET variables of CBF, CMRO2, OEF, CVR, and OEFR. The patients are followed for 2 years with visits every 3 months for a thorough neurologic examination and neurologic scoring i.e., NiH stroke scale (NIHSS), modified Rankin, Barthel Index and Quality of Life. Whenever a patient suffers a new clinical stroke, or at the end of the 2-year follow-up period, a second MRI is obtained and new cortical and subcortical infarcts are volumetrically quantitated. The stroke rate for patients in different stages of hemodynamic compromise is determined and compared along with the distribution of cortical, subcortical, paraventricular, and deep white matter infarctions by MRI to determine whether the patients in Stage Ill-chronic remain at risk for stroke.